Research On Coordinated Control Of Island DC Microgrid With Photovoltaic And Energy Storage

Compared with traditional power grid,DC microgrid has the advantages of flexible access to distributed power generation,wide application range and high conversion efficiency,and effectively solves the problem of new energy power generation consumption,thus attracting extensive attention from scholars at home and abroad.However,as a new type of power grid structure,dc microgrid has some problems such as low energy utilization rate and poor voltage stability of DC bus.The main technical means to solve this problem is to participate in the operation regulation of DC microgrid through source-storage-charge.In this paper,the PV and energy storage DC microgrid suitable for remote areas or independent power distribution areas is taken as the research object,and the coordinated control scheme and the control mode of each microgrid unit are studied in order to further improve the energy utilization rate and bus voltage stability of this kind of DC microgrid.After analyzing the operation characteristics and basic control principles of the optical storage DC microgrid architecture and component units,considering the problems of large electromagnetic interference and poor engineering economy of communication lines installed in each unit.In the overall control strategy of the system,a decentralized control scheme based on DC-Bus Signaling（DBS）with hysteresis control is designed.The scheme divides the permissible operating range of DC bus voltage into five operating ranges,and sets different operating modes of lightstorage-charge units in each operating range.The scheme not only has no communication connection between each unit,but also satisfies the timeliness and reliability of voltage and power regulation.In terms of microgrid cell control mode,aiming at the power reduction mode of photovoltaic cell,an improved control mode combining constant voltage control and U-P droop control is proposed to realize the photovoltaic power supply operation without light when the system power redundancy is large.A charging and discharging method based on fuzzy-droop was proposed for three charging and discharging modes of energy storage unit.This method can adjust the droop coefficient according to the State of Charge（SOC）deviation and bus voltage deviation,and realize the adaptive change of Charge and discharge rate.The coordination of the three operating modes of the energy storage unit not only improves the regulating ability of the energy storage unit,but also increases the working life.By classifying and modeling the load characteristics of dc microgrid application area,the types and sizes of batch switching load are determined,and the load regulation ability is improved.In order to verify the coordination of the improved control method of each microgrid unit,the simulation model of optical storage DC microgrid is established in Matlab/Simulink,and the actual operating conditions are simulated by changing the light intensity and load power,so that the microgrid can operate or switch freely under five voltage ranges.Simulation results show that the control strategy has good coordination,short transition time and high smoothness.